The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. Some carrier heads include a flexible membrane that provides a mounting surface for the substrate, and a retaining ring to hold the substrate beneath the mounting surface. Pressurization or evacuation of a chamber behind the flexible membrane controls the load on the substrate. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem in CMP is non-uniform polishing, i.e., the tendency of some portions of the substrate to be polished at a different rate than other portions of the substrate. This non-uniform polishing may occur even if pressure is applied uniformly to the substrate.
In one aspect, the invention is directed to a carrier head having a base, a first flexible membrane extending beneath the base to form a first pressurizable chamber, a support structure positioned in the first chamber, and a compressible film adjacent a bottom surface of the support structure. A lower surface of the first flexible membrane providing a mounting surface for a substrate. The compressible film has a plurality of apertures disposed in a pattern to establish a pressure distribution on a top surface of the first flexible membrane.
Implementations of the invention may include the following features. The pattern of the plurality of apertures may be selected to provide a non-uniform pressure distribution that improves polishing uniformity. The apertures may be disposed in a generally symmetric pattern, and may be less than about one-half inch in diameter. A second pressurizable chamber formed by a second flexible membrane may apply a downward pressure to the support structure.
In another aspect, the invention is directed to a carrier head having a base, a flexible membrane extending beneath the base and providing a mounting surface for a substrate, a support structure between the base and the flexible membrane, and a compressible film between the support structure and the flexible membrane. The compressible film includes a plurality of apertures to establish a pressure distribution across a surface of the substrate.
In another aspect, the invention is directed to a carrier head having a housing, a rigid structure movably connected to the housing, and a compressible film positioned on a bottom surface of the rigid structure. The compressible film has a plurality of apertures disposed in a pattern to create a pressure distribution across a surface of a substrate during polishing.
In another aspect, the invention is directed to a carrier head having a housing, a rigid structure movably connected to the housing, a plurality of indentations formed in a bottom surface of the rigid structure, and a compressible film positioned on the bottom surface of the rigid structure. The indentations in the rigid structure are disposed in a pattern to create a pressure distribution across a surface of a substrate during polishing.
In another aspect, the invention is directed to a carrier head having a housing, a rigid structure movably connected to the housing, and a compressible film positioned on a bottom surface of the rigid structure. The compressible film includes a plurality of regions of different compressibility. The regions of different compressibility are disposed in a pattern to create a pressure distribution across a surface of a substrate during polishing.
Implementations of the previous three embodiments may include the following. The carrier head may have a flexible membrane with a substrate receiving surface. The film may be positioned between the rigid structure and the flexible membrane.
In another aspect, the invention is directed to a compressible film that is detachably securable to a surface of a rigid structure in the carrier head. The compressible film has a plurality of apertures positioned to create a non-uniform pressure distribution on a substrate during polishing so as to improve polishing uniformity.
In another aspect, the invention is directed to a kit that has a carrier head with a housing and a rigid structure movably connected to the housing, and a plurality of compressible films detachably securable to a bottom surface of the rigid structure. Each compressible film has a plurality of apertures to create a non-uniform pressure distribution on a substrate during polishing. At least two of the compressible films have apertures disposed in different patterns to create different pressure distributions on the substrate.
In another aspect, the invention is directed to a carrier head that has a housing, a rigid structure movably connected to the housing, a compressible film secured to a surface of the rigid structure for transferring pressure to a substrate during polishing, and means for creating a non-uniform pressure distribution on the substrate from the compressible film.
Advantages of the invention may include the following. A non-uniform pressure can be applied to the back surface of the substrate to compensate for non-uniform polishing rates. Non-uniform polishing of the substrate is thereby reduced, and the resulting flatness and finish of the substrate are improved. A carrier head can easily be modified to provide different pressure distributions on the substrates.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.